1. Field of the Invention
The present invention generally relates to video display devices. The present invention specifically relates to a construction of gamma lookup tables for providing inversion flicker compensation to a liquid crystal display device.
2. Description of the Related Art
FIG. 1 illustrates a conventional LCD device 13 for transmitting a luminous output 14 in response to voltage drive signals VAS4-AS6 in analog form. FIG. 2 illustrates an exemplary luminance transmission percentage of luminous output 14 in terms of a red color component, a green color component, and a blue color component as a function of various levels of voltage drive signals VAS4-AS6. As known in the art, each drive voltage signal VAS4-AS6 is applied to each column (not shown) of corresponding LCD panels (not shown) of LCD device 13. Each column is connected via a transistor (not shown) to each pixel (not shown) in each row (not shown) of each LCD panel. LCD device 13 also includes a top plate (not shown) known as a counter electrode for each LCD panel. Each counter electrode receives a voltage reference signal VREF in analog form.
For the liquid crystal material within each pixel of each LCD panel to operate properly, the level of drive voltage signals VAS4-AS6 are modulated relative to voltage reference signal VREF. For example, if voltage reference signal VREF has a level of six (6) volts, then the levels of voltage drive signals VAS4-AS6 traverse a range from zero (0) volts to twelve (12) volts as shown in FIG. 2. A low inversion polarity range for voltage drive signals VAS4-AS6 is between zero (0) volts and six (6) volts. A high inversion polarity range for voltage drive signals VAS4-AS6 is between six (6) volts and twelve (12) volts. Frame inversion implies the levels of voltage drive signals VAS4-AS6 are within the low inversion polarity range for one video frame, the levels of voltage drive signals VAS4-AS6 are within the high inversion polarity range for a successive video frame, and so on, and so on.
Gamma circuit 10 includes conventional gamma lookup tables (not shown) for facilitating a reception of voltage drive signals VAS4-AS6 by LCD device 13 whereby, as shown in FIG. 3, LCD device 13 transmits luminous output 14 at a desired luminance response as related to voltage data signal VDS1-DS3 in digital form. Voltage data signal VDS1-DS3 are indicative of a particular gray level input from a conventional video source (not shown) as related to the red color component, the green color component, and the blue color component, respectively. For example, voltage data signal VDS1-DS3 can consist of eight bits representing 256 gray levels over a range of 00000000 (normalized as 0 in FIG. 3) to 11111111 (normalized as 1 in FIG. 3).
In response to a reception of voltage data signal VDS1-DS3, gamma circuit 10 obtains levels for voltage drive signals VAS4-AS6 for the low inversion polarity range that corresponds to the levels of voltage data signal VDS1-DS3, respectively. A digital-to-analog converter (DAC) 11 transform voltage data signal VDS1-DS3 to voltage drive signals VAS1-AS3, respectively, in analog form that is only provided with levels within the low inversion polarity range based on an average luminance response of luminous output 14 in both inversion polarity ranges. Thus, to achieve frame inversion, a voltage inversion circuit 12 provides voltage drive signals VAS4-AS6 in response to voltage drive signals VAS1-AS3, respectively, with the levels of voltage drive signals VAS4-AS6 being within the low inversion polarity range (e.g., equating control voltage VAS1) for one video frame, the levels of voltage drive signals VAS4-AS6 being within the high inversion polarity range (e.g., (2*VREF)xe2x88x92VAS1) for a successive video frame, and so on, and so on.
Luminous output 14 experiences an inversion flicker whenever one or more voltage drive signals VAS4-AS6 are attenuated prior to being applied to the appropriate pixels with LCD device 13. As known in the art, such attenuation typically occurs within conventional LCD device 13 whenever levels of voltage drive signals VAS4-AS6 are within the high inversion polarity range. Consequently, as exemplary illustrated in FIG. 4, a time-based amplitude measurement of luminous output 14 as related to each gray level input indicated by the levels of the voltage data signals VDS1-DS3 would exhibit uneven peaks relative to an average luminous response of luminous output 14 with the uneven peaks being representative of the inversion flicker.
Clearly, a disadvantage of employing gamma circuit 10, DAC 11, and voltage inversion circuit 12 to drive LCD device 13 is the failure to compensate for any occurrence of an inversion flicker of luminous output 14. Therefore, there is a need to provide a method and a device for eliminating inversion flicker within LCD device 13. The present invention addresses this need.
The present invention relates to a method and a device for eliminating inversion flicker within a LCD device. Various aspects of the present invention are novel, non-obvious, and provide various advantages. While the actual nature of the present invention covered herein can only be determined with reference to the claims appended hereto, certain features, which are characteristic of the embodiments disclosed herein, are described briefly as follows.
A first form of the present invention is a device comprising a LCD device operable to emit a luminous output in response to a reception of a voltage drive signal and a voltage reference signal. The device further comprises a display driver operable to provide the voltage drive signal to the LCD device in response to a reception of a voltage data signal having a data voltage level indicative of a gray level. The display driver includes a gamma lookup table for the voltage drive signal with the gamma lookup table listing a pair of drive voltage levels for the voltage drive signal that correspond to the gray level as indicated by a data voltage level of the voltage data signal. The drive voltage levels for the voltage drive signal have opposing polarities relative to a reference voltage level of the voltage reference signal.
A second form of the present invention is a method for applying an inversion flicker compensation to a luminous output being emitted by a liquid crystal display device in response to a reception of a voltage drive signal and a voltage reference signal. First, a display driver is operated to receive a voltage data signal having a data voltage level indicative of a first gray level. Second, the display driver is operated to obtain a pair of drive voltage levels for the voltage drive signal in response to the reception of the voltage data signal having the data voltage level. The pair of drive voltage levels having opposing polarities relative to a reference voltage level of the voltage reference signal. Finally, the display driver is operated to provide the voltage drive signal to the liquid crystal display device in a frame inversion manner involving the pair of drive voltage levels during a duration of the data voltage level indicating the first gray level.
The foregoing forms and other forms, features and advantages of the present invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the present invention rather than limiting, the scope of the present invention being defined by the appended claims and equivalents thereof.